1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus, such as a copier or a printer.
2. Description of the Related Art
Electrophotographic image forming apparatuses including an image bearing member and an intermediate transfer member have been developed. Such an existing image forming apparatus applies a voltage from a voltage power source (a power circuit) to a primary transfer member disposed so as to face the image bearing member with the intermediate transfer member therebetween. Thus, the image forming apparatus generates a primary transfer potential in a primary transfer section in which the intermediate transfer member is in contact with the image bearing member. In this manner, by using a potential difference formed between the image bearing member and the intermediate transfer member, the image forming apparatus primarily transfers a toner image formed on a surface of the image bearing member onto the intermediate transfer member (a primary transfer step). Subsequently, the primary transfer step is repeated for each of toner colors. In this manner, toner images having different colors are formed on the surface of the intermediate transfer member. Thereafter, a second transfer step is performed. In the second transfer step, the toner images having different colors and formed on the surface of the intermediate transfer member are simultaneously secondarily transferred onto a surface of a recording medium (e.g., a sheet of paper) by applying a secondary transfer voltage to the secondary transfer member. Thereafter, the toner images that are simultaneously transferred are fixed to the recording medium using a fixing unit.
Japanese Patent Laid-Open No. 2001-175092 describes the following structure. That is, a belt is used as the intermediate transfer member (hereinafter referred to as an “intermediate transfer belt”). A transfer power supply for primary transfer is connected to one of a stretching member that keeps the inner circumferential surface of the intermediate transfer belt tight and the primary transfer member. By passing an electric current in the circumferential direction of the intermediate transfer belt, a voltage is applied from a single transfer power supply to a plurality of primary transfer members.
However, in Japanese Patent Laid-Open No. 2001-175092, a power supply for primary transfer and a power supply for secondary transfer are provided so as to be independent from each other. That is, the power supply for primary transfer and the power supply for secondary transfer are not made common.